Gas turbines are widely used in industrial, marine, aircraft and power generation operations. A gas turbine includes a compressor section, a combustion section disposed downstream from the compressor section, and a turbine section disposed downstream from the combustion section. In particular configurations the gas turbine is at least partially disposed within an enclosure. Generally, the enclosure protects the gas turbine from resident environmental conditions, reduces acoustic emissions from the gas turbine and insulates the immediate surroundings from heat emanating from the gas turbine during operation.
A ventilation system draws air into the enclosure through one or more inlet ducts, across the turbine and exhausts the air through one or more exhaust ducts, thereby reducing thermal build up within the enclosure and/or removing hazardous gases such as methane or other potentially explosive gases that may leak from the various fuel and/or exhaust connections defined within the enclosure. A hazardous gas detection system is deployed within and/or proximate to the exhaust duct to detect or measure hazardous gas concentrations such as methane or other explosive gas concentrations within the exhaust air flowing through the exhaust duct.
Analysis has shown that concentrations of hazardous gas are highly stratified within the exhaust duct. In other words, the concentration of the hazardous gas is not uniform across an exhaust air flow area defined within the exhaust duct. Therefore, particular hazardous gas detection systems utilize a redundancy method for achieving high reliability and availability of the gas turbine by preventing false alarms and/or controlled shut downs or trips of the gas turbine which may otherwise result from a single point or single sensor failure.
For example, in order to guarantee that two sensors will always be in the hazardous gas flow field particular hazardous gas detection systems utilize three or four sensors arranged in an array along a grid or otherwise spaced across the flow area of the exhaust duct. A computing device or controller receives a signal from each of the sensors that is indicative of the hazardous gas concentration at each sensor location within the exhaust duct flow area.
The computing device utilizes a two out-of three or two out-of four control logic to insure that at least two of the sensors from different locations in the exhaust air flow area are operational and detecting sufficiently high enough concentration levels of the hazardous gas to warrant an alarm, a controlled shut down or trip of the gas turbine. This is required to prevent a trip or shut down due to a single sensor failure and/or a single sensor reading a relatively high concentration of the hazardous gas which may not represent the overall hazardous gas concentration within the exhaust duct flow area.
Multiple sensors placed within the exhaust air flow field results in increased costs and complexity to install, maintain and operate. Proper positioning of each sensor is critical to prevent false alarms and/or unnecessary trips of the gas turbine. However, defining the proper location within the exhaust duct requires highly complicated computational fluid dynamics models which may vary from actual operating conditions. Furthermore, each sensor presents a failure opportunity, thus potentially resulting in an unnecessary trip or shut down of the gas turbine which affects the overall reliability of the system. Therefore, an improved hazardous gas system for a gas turbine enclosure would be useful.